The present invention relates to variable valve actuating mechanisms and, more particularly, to a variable valve actuating mechanism that enables adjustment of the amount by which one valve is lifted relative to another valve within the same engine cylinder.
Modern internal combustion engines may incorporate advanced throttle control systems, such as, for example, intake valve throttle control systems, to improve fuel economy and performance. Generally, intake valve throttle control systems control the flow of gas and air into and out of the engine cylinders by varying the timing and/or lift (i.e., the valve lift profile) of the cylinder valves in response to engine operating parameters, such as engine load, speed, and driver input. For example, the valve lift profile is varied from a relatively high-lift profile under high-load engine operating conditions to a reduced/lower low-lift profile under engine operating conditions of moderate and low loads.
Intake valve throttle control systems vary the valve lift profile through the use of various mechanical and/or electromechanical configurations, collectively referred to herein as variable valve actuation mechanisms. Several examples of particular variable valve actuation mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference. A variable valve actuation mechanism varies the lift profiles of one or more associated valves from a high-lift profile under high-load engine operating conditions to a reduced/lower low-lift profile under engine operating conditions of moderate and low loads. The valves may be lifted, for example, 8-10 millimeter (mm) under the high-lift profile and 1.0 mm or less under the low-lift profile. Contemporary engines typically include 4 valves per cylinder, i.e., two intake valves and two exhaust valves. The engine may be variously configured, such as, for example, with one variable valve actuation mechanism per cylinder that actuates both intake valves of that cylinder or configured with two variable valve actuation mechanisms per cylinder each of which actuate a corresponding pair of intake or exhaust valves.
Variable valve actuating mechanisms may be manually adjusted during installation in order to match the peak lifts of valves in different cylinders. Matching the peak valve lifts of valves in different cylinders increases engine stability and reduces rough engine operation, especially at low peak lift operating conditions. Matching the peak lifts ensures each of the valves is opened the same amount and, thus, each cylinder produces approximately the same amount of power. Although the peak lifts of valves of different cylinders can be matched, conventional variable valve actuating mechanisms do not enable the adjustment and/or matching of peak valve lifts of the valves associated with an individual engine cylinder. Thus, the peak lifts of the valves associated with an individual engine cylinder may be undesirably mismatched.
An undesirable mismatch between the peak lifts of valves associated with an individual engine cylinder is generally attributable to dimensional variation, and will typically be in the range of from approximately 1.0 mm to approximately 0.5 mm or less. When the valves are actuated such that their peak lifts are relatively high, such as, for example, greater than 8 mm, such a mismatch constitutes a relatively small percentage of the peak lift. However, under certain engine operating conditions, such as, for example, engine idle and low speed engine operating conditions, the valves are actuated such that their peak lift is relatively small, such as, for example, from approximately 0.5 millimeters (mm) to approximately 1.0 mm of peak lift. At such relatively low peak lift amounts, such a mismatch constitutes a substantial and significant percentage of the peak valve lift. Thus, the mismatch in lifts becomes proportionally greater as the peak lifts decrease.
A mismatch between the peak lifts of the valves associated with an individual engine cylinder can result in undesirable or unintended airflow characteristics, such as, for example, reduced tumble and/or excessive swirl. Since the mismatch becomes proportionally greater relative to the peak valve lift as the peak valve lift decreases, these undesirable characteristics are also magnified as the peak valve lifts decrease.
Therefore, what is needed in the art is an apparatus and method that enables the peak valve lifts within a cylinder to be adjusted and, thus, set or calibrated to within a relatively close or desired tolerance.
Furthermore, what is needed in the art is an apparatus and method that enables the peak valve lifts within a cylinder to be matched to within a relatively close tolerance at low peak lift engine operating conditions.
The present invention provides a variable valve actuating mechanism that enables independent adjustment of the peak lift of one valve relative to another valve actuated by the same mechanism.
The invention comprises, in one form thereof, a frame member and a rocker. The rocker includes a first end and a second end, with the first end being pivotally coupled to the frame. A link includes a first end and a second end. A first pin pivotally couples the first end of the link to the second end of the rocker. A second pin pivotally couples an output cam to the second end of the link. At least one of the first and second pins is an eccentric pin.
An advantage of the present invention is that the peak valve lift of one valve relative to another valve within the same cylinder is adjustable.
A further advantage of the present invention is that the peak lifts of the valves within a cylinder are matched and/or set to within a relatively close tolerance.
A still further advantage of the present invention is that tumble and/or swirl within a cylinder is adjusted by adjusting the relative lifts of the valves within the cylinder.
An even further advantage of the present invention is that the peak lifts of the valves within a cylinder are matched to within a relatively close tolerance at low peak lift engine operating conditions.